/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */

struct ListNode
{
    int val;
    ListNode next;
    ListNode(int x) : val(x), next(NULL) {}
};
class Solution
{
public:
    bool hasCycle(ListNode *head)
    {
        ListNode *fast = head, *slow = head;
        while (fast->next != NULL && slow != NULL)
        {
            fast = fast->next->next;
            slow = slow->next;
            if (fast == slow)
                return true;
        }
        return false;
    }
};